8.6. What are itee and sugee?

In slangy or rough speech, i adjectives (see 2.4.2. What is an i adjective?) and
na adjectives ending in ai or oi often change to ee
endings. For example, sugoi, an i adjective meaning "amazing",
becomes sugee, and karai, a na adjective meaning "hot,
spicy", becomes karee. Similarly, itai becomes
itee. Urusai, meaning "noisy" or "shut up" (see
8.5. What are some Japanese insults and swear-words?) becomes urusee, hence the pun in the name of the
manga Urusei Yatsura (うる星やつら).

This is usually a spoken form, but when written down, it is often
written either with a small kana え, as in いてぇ, or a wavy line,
いてぇ〜.

Any adjective ending in ai or oi can take this
pattern. Negative verbs ending in nai can also change, as in
iranee for iranai.

Adjectives ending in ui, such as warui, "bad", change to
warii, similarly akarui becomes akarii. This is not as
common as the oi, ai change to ee though.